The standardization of IEEE802.11e is currently developing as an extension of the IEEE802.11 standard (see the following non-patent document 1). The IEEE802.11e standard adds HCF (Hybrid Coordination Function) and defines HC (Hybrid Coordinator). The HCF is extended by combining DCF (Distributed Coordination Function) and PCF (Point Coordination Function) to have QoS (Quality of Service) specific mechanisms and frame subtypes which enable frame exchange sequences for QoS transmission between CP (Contention Period) and CFP (Contention Free Period).
The HC operates based on different rules from those for PC (Point Coordinator) in PCF. The HC coexists with a QoS enhanced access point (QAP: Quality enhanced Access Point) in QBSS (QoS Basic Service Set). The HC uses high access priority to a wireless medium of a PC to start a frame exchange sequence in order to give a controlled access phase (CAP) of a predetermined period for transfer of QoS data. Thus, the HC assigns transmit opportunities (TXOP) to QoS enhanced stations (QSTA) that are not access points. Access is prioritized by each period of waiting time during which an idle physical channel is being detected. A normal terminal needs to wait for a period equivalent to DIFS (DCF Interframe Space). On the other hand, the HC uses as the waiting time a period equivalent to PIFS (PCF Interframe Space) usually shorter than the DIFS.
Non-patent document 1: IEEE Std 802.11e/D4.2, February 2003 (Draft Supplement to IEEE Std 802.11, 1999 Edition).
However, there exists no process for controlling the operation of an HC under circumstances where QBSSs overlap. For example, if two HCs share the same time on a wireless medium, both HCs may try to access the wireless medium at the same time. After a signal collision occurs due to simultaneous access, both of the HCs wait for the same time period (PIFS). After that, they will try to access at the same time again, causing a recollision. Such a process may persist endlessly.
Thus, the conventional art has a problem in that an HC is not aware of or cannot make an effective response to the existence of any other HC, for example, when QBSSs are overlapping. There is also another problem in that if two or more HCs try to access a wireless medium, transmission from the HCs may collide repeatedly and intermittently.